1. Field of the Invention
The invention relates generally to the automatic cancellation of external magnetic fields and, in particular, to apparatus for compensating for an external magnetic field affecting the operation of a cathode ray tube (CRT) display.
2. Description of the Prior Art
Frequently it is necessary to operate a CRT display in the presence of a five gauss axial external magnetic field. With only a degaussing network in conjunction with a shield around the CRT, a 1.5 to 2 gauss axial field may be effectively cancelled. It has been suggested that Hall effect devices and fluxgate transformers may be used in conjunction with active circuitry to cancel external magnetic fields. However, these methods are very complex and high in cost.